EPA cannot wait for scientific certainty before it sets an air quality standard, the Center for Biological Diversity, the Clean Air Council, and the National Parks Conservation Association said Nov. 30 in an opening brief filed in the U.S. Court of Appeals for the District of Columbia Circuit.

The agency has acknowledged the existing secondary national ambient air quality standards, which were set in 1971, do not adequately protect the environment from the indirect effects of acid rain and other forms of acid deposition. However, in an April 3 final rule at 40 C.F.R. pt. 50, it retained the existing standards, saying it did not have enough information to set new standards and is planning a five-year field pilot program to collect data to help in the future development of a multi-pollutant standard (77 Fed. Reg. 20,218; 55 DEN A-1, 3/22/12).

“The statute does not limit EPA's standard-setting duty to situations where data are complete and uncertainties eliminated,” the petitioners told the D.C. Circuit. “Rather, EPA must use its best judgment to specify, based on its review of the relevant factors and advice from the Scientific Advisory Committee, a standard that meets the statutory mandate despite remaining uncertainty.”

The petitioners asked the court to vacate the final rule and remand it to the agency to set a new standard within 14 months.Standards Protect Against Direct Effects.

EPA sets primary national ambient air quality standards to protect public health and secondary standards to protect the environment and public welfare.

The 1971 secondary standards for nitrogen dioxide and sulfur dioxide are intended to protect the environment against the direct effects of the pollutants, not the indirect effects of acid rain and other forms of acid deposition. Nitrogen dioxide and sulfur dioxide are the primary precursors to acid rain.

The petitioners said the Clean Air Act requires EPA to set secondary standards that protect against any known or anticipated adverse effects on public welfare.

The brief said the agency retained standards that it “concedes do not provide requisite protection against acknowledged harm from deposition of air pollutants. The agency's violation of the statute could not be clearer.”

The secondary standard for nitrogen dioxide is 0.053 part per million, averaged annually. The standard for sulfur dioxide is 0.5 ppm, averaged over three hours and not to be exceeded more than once annually.

EPA Administrator Lisa Jackson signed the final rule March 20 under the terms of a 2007 consent decree that resolved a lawsuit brought by the Center for Biological Diversity over EPA's inaction on reviewing the standards (Center for Biological Diversity v. Jackson, D.D.C, No. 05-1814, notice filed 8/30/12).Reasoning Not Explained.

In a 2011 policy assessment, EPA staff recommended that revisions to the secondary standards be based on maintaining an acid-neutralizing capacity in the environment between 20 microequivalents and 75 microequivalents per liter.

The petitioners also argued that EPA did not adequately explain why data gaps and modeling uncertainties are so profound to prevent it from setting a standard. The brief said neither EPA's staff nor its independent science advisers, the Clean Air Scientific Advisory Committee, recommended against setting a new standard.

“Put simply, the Administrator's excuses cannot be squared with the fact that the Scientific Advisory Committee and EPA's own staff explicitly laid out, in great detail, an ample basis for setting a standard providing requisite protection from aquatic acidification,” the brief said.

The brief said EPA staff analyzed acid-sensitive regions at various forms and levels in a range of the possible standards and found between eight and 25 regions would not meet the standard.

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